First of all, good piece! You asked a question as to why people give partial votes instead of full votes? I am not sure about others so I will explain why I just gave you a mere 30% vote. It is not because I only give you a score of 30/100 for this article, it is really because there are a limited number of votes I can give per day. Every vote I cast consumes my voting power which will only replenish 20% per day. Considering that, I have to "ration" my voting activities because there are many good articles that deserve my vote.

On AI. Artificial intelligence is a really broad term and it has been incorrectly used at times. Over here, what @trufflepig did is called machine learning. Machine learning basically takes past data and establish relationships within the data so that it can predict an outcome when it is fed a new set of data. It is an evolving area, but it has a major flaw of garbage in garbage out. The data model is only as good as the data it is fed.

Apart from machine learning, there are also other fields of AI. Such as natural language processing/generation, speech recognition, robotics and etc. Will AI replace humans one day? It's hard to say without a specific date. I think it probably won't happen in the near future. But who knows what will happen in 50 years or 100 years :)